Published patent application US2008/0238335A1, which is incorporated by reference, discloses in one specific embodiment a solid state light source comprising three Light Emitting Diodes (LEDs), a controller to control a light emission of the three LEDs and a photodetector. Two of the LEDs comprise the same type of blue emitting LED die and they both comprise the same type of (yellow emitting) luminescent material, but in other quantities. These two LEDs both have a color point not far away from the black body line one of the two color points is above the black body line and one of the two color points is below the black body line. The third LED is configured to emit green light. The document discloses that the light emission of the third LED is a combination of light emitted by a LED die and one or more luminescent materials. The controller receives from the photo detector a signal that indicates characteristics of the light emitted by the solid state light source. Subsequently the controller controls the individual light emissions of the LEDs to obtain a required light emission by the solid state light source which is a predefined or controllable point on the black body line.
A disadvantage of the embodiment of the cited patent application is that the color points of two LEDs, which have their color points close to the black body line, are on a line between a color point of the blue emitting LED die and a color point of the light emitted by the specific luminescent material. In such a situation it is impossible to select the two LEDs such that their color point are close to the black body line and such that a wide range of correlated color temperatures can be emitted by the solid state light source. Thus, only a small portion of the black body line is within a triangle defined by the color points of all three LEDs. Also the fact that one of the color points of one of the two LEDs is above the black body line contributes to the fact that a relatively small portion of the black body line is in a triangle defined by the color points of all three LEDs.